1. Field of the Invention
This invention relates to a method of manufacturing an integral rotor blade disk, commonly referred to as a blisk and to blisks of characteristic shape produced in accordance with the method. A blisk comprises a hub and a plurality of blades integrally projecting substantially radially therefrom.
2. Summary of the Prior Art
The machining of the blades of a blisk from a solid disk in the raw state involves preliminary machining of the disk using a milling cutter with a large radius to leave blade blanks that have to be machined more finely to a definitive shape. It is common practice to resort to milling to perform this fine machining. Milling cutters used for this purpose have a special conical shape, and taper toward a rounded end allowing high-precision machining operations to be performed.
One known method is end milling in which the rotation spindle of the milling cutter is oriented radially with respect to the disk and rotates about each of the blades advancing gradually toward the hub of the disk, machining the blade in a helical path. The rotation spindle of the milling cutter is, in actual fact, inclined slightly so as to be away from the machined blade and so as to perform the machining essentially using the rounded end of the milling cutter. The height of pass, that is to say the pitch of the helix, is about half a millimeter, which means that the machining of a blade is not completed until several hundreds of passes have been made. This method is therefore fairly lengthy, and this limits the height of the blades to which it can be applied.
Another known milling method uses a milling cutter of the same conical shape, still rounded at the end, but with a longer conical part. As before, the milling cutter is arranged radially, but here, the end of the blade is milled with the conical part in a single broad tangential pass and then the root of the blade is, as previously, milled mainly using the end of the milling cutter in small passes. The broad pass saves time over the previous method even if the rate of advance of the tool has to be lowered; however, the swifter milling is accompanied by blade vibration and flexing which make it unsuitable for relatively tall blades. Furthermore, this method is more tricky to perform because of the risk of hollowing of the blade that additional unintentional machining by the conical part on an already-machined portion may cause.